Aortic stenosis is a condition in which the aortic valve has become stenotic (narrowed) and does not open normally. The aortic valve is located between the left ventricle of the heart and the aortic arch. The aortic arch leads to the ascending and descending aorta as well as other major blood vessels and is the main blood vessel that supplies oxygen rich blood to the rest of the body. When the aortic valve is stenotic, the ability of the left ventricle to pump blood out of the heart into the aorta and other arteries is impaired. The body's organs including the brain may then receive an insufficient supply of oxygen rich blood and blood may tend to back-up into the lungs causing shortness of breath.
The aortic valve is a tricuspid valve. That is, it has three leaflets or flaps that open and close. The function of the aortic valve is to allow blood to flow only out of the left ventricle and into the aorta when the left ventricle is contracting. When the heart muscle relaxes, the aortic valve closes, thus preventing blood from the aorta from flowing back into the left ventricle. When a patient has aortic stenosis, the leaflets of the aortic valve become thickened and calcified. Historically, a common cause of aortic stenosis was patients who had rheumatic fever during childhood. Other patients developed symptoms of aortic stenosis when they are in their 40's or 50's because of a genetically determined defect in which the aortic valve has two leaflets instead of three. By far, the most common cause of aortic stenosis is age related degeneration and calcification of the aortic valve. Typically, degenerative aortic stenosis begins to manifest symptoms when patients are more than 70 years old.
When the aortic valve becomes stenotic, the volume of blood pumped out of the left ventricle is reduced. The heart tissue then tends to hypertrophy to compensate for the increased effort necessary to pump blood out of the left ventricle. This ventricular hypertrophy leads to an enlarged heart. Ultimately, the left ventricle looses flexibility, tends to dilate and becomes even less efficient at pumping blood into the aorta. In some cases, the aortic valve becomes so stenotic that blood flow to the brain is dramatically reduced causing syncope. In addition, aortic stenosis patients often suffer from angina. Finally, patients with aortic stenosis tend to demonstrate shortness of breath because of the accumulation of blood in the lungs. Patients with severe aortic stenosis may require replacement of the aortic valve with a prosthetic heart valve.
One way to gauge the severity of aortic stenosis is to measure the pressure differential between the left ventricle and the aortic arch, across the aortic valve. Measuring differential pressure across the aortic valve to diagnosis aortic stenosis is a known procedure. One such technique for measuring differential pressures across the aortic valve utilizes a catheter that has an eight French diameter along its entire length and two parallel side-by-side lumens of unequal size. This catheter incorporates a perforated metal plate in the distal segment of the smaller lumen that allows fluid communication for measuring pressure in the aorta. The larger lumen of this catheter incorporates distal side holes that allow fluid communication for measuring pressure in the left ventricle. The smaller lumen is perforated on one side only and can lead to distorted pressure reading if the perforations impinge on the wall of the aorta as the pressure wave of aortic systole moves past the catheter. The side-by-side arrangement of the catheter tends to make the catheter less flexible and more difficult to maneuver. In addition, the durometer of the eight French distal tip is not always soft enough to conform to a guide wire.
Pigtail catheters are known in the art. A pigtail is a coiled or spiral portion at the terminal end of a catheter. The coil generally approximates three hundred sixty degrees but may be somewhat more or less than this value. A pigtail design presents a blunt, smooth, resilient end to body tissue into which it comes in contact reducing the risk of damage to tissues that the end of the catheter comes into contact with.
It would be a benefit to the diagnostic arts if there was available a differential pressure measuring catheter that was flexible enough to consistently conform to a guide wire and whose pressure measuring qualities were less effected by impingement on the vascular tissues.